Low pressure plasma spraying is well suited for high-temperature corrosion-resistant coatings of gas turbine components. In this coating process, coating adhesion is an important problem, and so surface roughness and cleaning achieved by the transferred arc treatment with negative substrate polarity have to be investigated in order to improve the adhesion. In this paper, an experimental investigation was conducted to clarify the effect of the transferred arc treatment on the bonding strength of sprayed coatings. As a result, it was verified by SEM observations that surface cleaning and surface roughening could be made by the transferred arc treatment in case of IN738LC, SUS304, tungsten and copper. It was also confirmed that grit-blasting before the transferred arc treatment was effective for the uniformity of surface cleaning and roughening, which means to improve the adhesion of sprayed coating. And it was confirmed that the surface roughness achieved by the transferred arc treatment could be evaluated by thermal conduction parameter c·ρ·(Tm-T0), c; specific heat, ρ; density, Tm; melting point, T0; initial temperature.